feat: Set up PWA infrastructure with service worker, offline support, and manifest

- Created service worker (public/sw.js) with caching strategies
  - Cache-first strategy for static assets
  - Stale-while-revalidate for API responses and pages
  - Network-first fallback strategy
- Implemented offline fallback page (/offline)
- Updated manifest.json with complete PWA metadata
- Added service worker registration in app layout
- Created ServiceWorkerRegistration component for client-side registration
- Generated SVG icons for PWA (192x192 and 512x512)
- Added PWA meta tags for iOS Safari support

Validates Requirements: 4.1, 4.3, 4.4

public/icon-512.svg

@@ -0,0 +1,7 @@
+<svg width="512" height="512" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg">
+  <rect width="512" height="512" rx="128" fill="#3B82F6"/>
+  <path d="M153.6 256L230.4 332.8L358.4 179.2" 
+        stroke="white" stroke-width="40.96" stroke-linecap="round" stroke-linejoin="round"/>
+  <rect x="128" y="307.2" width="256" height="40.96" rx="10.24" fill="white"/>
+  <rect x="128" y="368.64" width="204.8" height="40.96" rx="10.24" fill="white"/>
+</svg>